Dynamics and consequences of IL-21 production in HIV-infected individuals: a longitudinal and cross-sectional study

The Role of Glutathione in the Management of Cell-Mediated Immune Responses in Individuals with HIV

Human immunodeficiency virus (HIV) is a major cause of death worldwide. Without appropriate antiretroviral therapy, the infection can develop into acquired immunodeficiency syndrome (AIDS). AIDS leads to the dysregulation of cell-mediated immunity resulting in increased susceptibility to opportunistic infections and excessive amounts of inflammatory cytokines. HIV-positive individuals also demonstrate diminished glutathione (GSH) levels which allows for increased viral replication and increased pro-inflammatory cytokine release, further contributing to the high rates of mortality seen in patients with HIV. Adequate GSH supplementation has reduced inflammation and slowed the decline of CD4+ T cell counts in HIV-positive individuals. We aim to review the current literature regarding the role of GSH in cell-mediated immune responses in individuals with HIV- and AIDS-defining illnesses.

IL-21-IgFc immunotherapy alters transcriptional landscape of lymph node cells leading to enhanced flu vaccine response in aging and SIV infection

Aging people living with HIV (PWH) frequently manifest impaired antibody (Ab) responses to seasonal flu vaccination which has been attributed to ongoing inflammation and immune activation. We have recently reported a similar scenario in old simian immunodeficiency virus (SIV) infected rhesus macaques (RM) with controlled viremia and have been able to compensate for this deficiency by immunotherapy with interleukin (IL)-21-IgFc. To understand the underlying mechanisms of IL-21-induced immunomodulation leading to enhanced flu vaccine response in aging and SIV, we have investigated draining lymph node (LN) cells of IL-21-treated and -untreated animals at postvaccination. We observed IL-21-induced proliferation of flu-specific LN memory CD4 T cells, expansion of B cells expressing IL-21 receptor (IL-21R), and modest expansion of T follicular helper cells (Tfh) co-expressing T-cell immunoreceptor with Ig and ITIM domains (TIGIT) and DNAX accessory molecule (DNAM-1). Transcriptional analysis of LN cells of IL-21-treated animals revealed significant inhibition of germinal center (GC) Tfh and B-cell interferon signaling pathways along with enhanced B-cell development and antigen presentation pathways. We conclude that IL-21 treatment at the time of flu vaccination in aging SIV-infected animals modulates the inductive LN GC activity, to reverse SIV-associated LN Tfh and B-cell dysfunction. IL-21 is a potential candidate molecule for immunotherapy to enhance flu vaccine responses in aging PWH who have deficient antibody responses.

The Role of CD4 T Cell Help in CD8 T Cell Differentiation and Function During Chronic Infection and Cancer

CD4 and CD8 T cells are key players in the immune response against both pathogenic infections and cancer. CD4 T cells provide help to CD8 T cells via multiple mechanisms, including licensing dendritic cells (DCs), co-stimulation, and cytokine production. During acute infection and vaccination, CD4 T cell help is important for the development of CD8 T cell memory. However, during chronic viral infection and cancer, CD4 helper T cells are critical for the sustained effector CD8 T cell response, through a variety of mechanisms. In this review, we focus on T cell responses in conditions of chronic Ag stimulation, such as chronic viral infection and cancer. In particular, we address the significant role of CD4 T cell help in promoting effector CD8 T cell responses, emerging techniques that can be utilized to further our understanding of how these interactions may take place in the context of tertiary lymphoid structures, and how this key information can be harnessed for therapeutic utility against cancer.

Interleukin-2 family cytokines: An overview of genes, expression, signaling and functional roles in teleost

The interleukin-2 (IL-2) family cytokines include IL-2, IL-4, IL-7, IL-9, IL-15, and IL-21, which share γ chain (γc) subunit in receptors. The IL-2 family cytokines have unique biological effects that regulate differentiation, survival and activation of multiple lymphocyte lineages. Deficiency of IL-2 family signaling pathway in mammals prevents CD4⁺ T cells from developing effector functions and CD8⁺ T cells from developing immunological memory. In the present review, we addressed available information from teleost IL-2 family cytokines and discussed implications in teleost immunity. Also, we described and discussed their expression profiles, receptors, signaling transductions and functions. In teleost, IL-2 family has 5 members (IL-2, IL-4/13, IL-7, IL-15, IL-21) without IL-9, and their receptors share a common γc subunit and include other 6 subunits (IL-2Rβ1/2, IL-4Rα1/2, IL-13Rα1/2, IL-7Rα, IL-15Rα, and IL-21Rα1/2). Some paralogues have changes in domain structure and show differential expression, modulation, functions. IL-2 family cytokines constitutively express in many immune associated tissues and are largely induced after pathogenic microbial stimulation. In general, there are relatively conserved functions in the IL-2 family throughout vertebrates, and many of the key IL-2 family members are important in lymphocyte proliferation and differentiation, development, inflammation from fishes to mammals. This review will give an update on the effective information of teleost IL-2 family cytokines. Thus, it will provide a source of reference for other researchers/readers and inspire further interest.

The Role of Innate Immunity in Natural Elite Controllers of HIV-1 Infection

The natural process of human immunodeficiency virus type 1(HIV-1) infection is characterized by high viral load, immune cell exhaustion, and immunodeficiency, which eventually leads to the stage of acquired immunodeficiency syndrome (AIDS) and opportunistic infections. Rapidly progressing HIV-1 individuals often die of AIDS several years after infection without treatment. The promotion of ART greatly prolongs the survival time of HIV-infected persons. However, some patients have incomplete immune function reconstruction after ART due to latent storage of HIV-infected cells. Therefore, how to achieve a functional cure has always been the focus and hot spot of global AIDS research. Fortunately, the emergence of ECs/LTNPs who can control virus replication naturally has ignited new hope for realizing a functional cure for AIDS. Recently, a special category of infected individuals has attracted attention that can delay the progression of the disease more rigorously than the natural progression of HIV-1 infection described above. These patients are characterized by years of HIV-1 infection, long-term asymptomatic status, and normal CD4+T cell count without ART, classified as HIV-infected long-term nonprogressors (LTNPs) and elite controllers (ECs). Numerous studies have shown that the host and virus jointly determine the progression of HIV-1 infection, in which the level of innate immunity activation plays an important role. As the first line of defense against pathogen invasion, innate immunity is also a bridge to induce adaptive immunity. Compared with natural progressors, innate immunity plays an antiviral role in HIV-1 infection by inducing or activating many innate immune-related factors in the natural ECs. Learning the regulation of ECs immunity, especially the innate immunity in different characteristics, and thus studying the mechanism of the control of disease progression naturally, will contribute to the realization of the functional cure of AIDS. Therefore, this review will explore the relationship between innate immunity and disease progression in ECs of HIV-1 infection from the aspects of innate immune cells, signaling pathways, cytokines, which is helpful to provide new targets and theoretical references for the functional cure, prevention and control of AIDS, and development of a vaccine.

Evaluation of several serum interleukins as markers for treatment effectiveness in naïve HIV infected patients: A pilot study

In this observational pilot study, we investigated the impact of Dolutegravir, Raltegravir, Elvitegravir (Integrase Strand Transfer Inhibitors, INSTIs), or boosted Darunavir (a Protease Inhibitor, PI) in combination with two nucleoside reverstranscriptase inhibitors (Emtricitabine/Tenofovir disoproxil or Lamivudine/Tenofovir disoproxil, NRTI) on four interleukins (IL-4, IL-10, IL-13, and IL-21) as immune activation markers in naïve HIV(Human Immunodeficiency Virus)-infected patients during the first six months of combined standard-of-care antiretroviral therapy (cART). Newly diagnosed with HIV-infected subjects and without any disease that could affect the immune activation markers were evaluated. The patients’ physicians recommended the cART as standard-of-care and the ILs were measured before cART and six months of cART. The levels of CD4⁺ T-cells count and CD4⁺/CD8⁺ ratio significantly increased at six months (P-value<0.02) regardless of the drugs, INSTIs or PI. However, a CD4⁺/CD8⁺ >1 was observed in 25% of patients treated with Raltegravir and half of those treated with Dolutegravir. At six months of cART, viral load was detectable in only 6/31 individuals. IL-21 had an undetectable level in 30/31 patients after six months of cART. Our results suggest the potency in restoring immune markers in HIV-infected patients with all investigated drugs. Dolutegravir showed a tendency to statistically significant changes in IL-4 and IL-10. A clinical trial with random allocation of medication and an extensive follow-up is needed to replicate this research and validate the usefulness of evaluated ILs as markers of cART effectiveness.

Autophagy-dependent glutaminolysis drives superior IL21 production in HIV-1-specific CD4 T cells

The maintenance of a strong IL21 production in memory CD4 T cells, especially in HIV-1-specific cells, represents a major correlate of natural immune protection against the virus. However, the molecular mechanisms underlying IL21 production during HIV-1 infection, which is only elevated among the naturally protected elite controllers (EC), are still unknown. We recently found out that lipophagy is a critical immune mediator that control an antiviral metabolic state following CD8A T cell receptor engagement, playing an important role in the natural control of HIV-1 infection. This led us to investigate whether the beneficial role of a strong macroautophagy/autophagy, could also be used to ensure effective IL21 production as well. Herein, we confirm that after both polyclonal and HIV-1-specific activation, memory CD4 T cells (Mem) from EC display enhanced activity of the autophagy-mediated proteolysis compared to ART. Our results indicate that the enhanced autophagy activity in EC was controlled by the energy-sensing PRKAA1 (protein kinase AMP-activated catalytic subunit alpha 1). We further confirmed the critical role of the autophagy-mediated proteolysis in the strong IL21 production in EC by using BECN1 gene silencing as well as protease, PRKAA1, and lysosomal inhibitors. Finally, we established that high autophagy-mediated proteolysis in EC fuels their cellular rates of mitochondrial respiration due to glutaminolysis. Our data confirm the critical role of autophagy in dictating the metabolic input, which is required not only to ensure protective cytotoxic CD8A T cell responses, but also to provide strong IL21 production among antiviral CD4 T cells.Abbreviations: AKG: alpha-ketoglutarate; ART: patients under antiretroviral therapy; ATG7: autophagy related 7; BaF: bafilomycin A₁; BECN1: beclin 1; Chloro.: chloroquine; EC: elite controllers; EIF4EBP1: eukaryotic translation initiation factor 4E binding protein 1; FOXO3: forkhead box O3; GLS: glutaminase; GLUD1: glutamate dehydrogenase 1; HIV^neg: HIV-1-uninfected control donors; IFNG/IFN-γ: interferon gamma; IL21: interleukin 21; MTOR: mechanistic target of rapamycin kinase; PBMC: peripheral blood mononuclear cells; PRKAA1: protein kinase AMP-activated catalytic subunit alpha 1; SQSTM1: sequestosome 1; TCA: tricarboxylic acid cycle; ULK1: unc-51 like autophagy activating kinase.

Interleukin-21 in Viral Infections

Interleukin (IL)-21 is a cytokine that affects the differentiation and function of lymphoid and myeloid cells and regulates both innate and adaptive immune responses. In addition to regulating the immune response to tumor and viral infections, IL-21 also has a profound effect on the development of autoimmune and inflammatory diseases. IL-21 is produced mainly from CD4⁺ T cells-in particular, follicular helper T (Tfh) cells-which have a great influence on the regulation of antibody production. It is also an important cytokine for the activation of CD8⁺ T cells, and its role in recovering the function of CD8⁺ T cells exhausted by chronic microbial infections and cancer has been clarified. Thus, IL-21 plays an extremely important role in viral infections, especially chronic viral infections. In this review, I will introduce the findings to date on how IL-21 is involved in some typical viral infections and the potential of treating viral diseases with IL-21.

HIV-1 infection and the lack of viral control are associated with greater expression of interleukin-21 receptor on CD8+ T cells

OBJECTIVES

Interleukin-21 (IL-21) has been linked with the generation of virus-specific memory CD8+ T cells following acute infection with HIV-1 and reduced exhaustion of CD8+ T cells. IL-21 has also been implicated in the promotion of CD8+ T-cell effector functions during viral infection. Little is known about the expression of interleukin-21 receptor (IL-21R) during HIV-1 infection or its role in HIV-1-specific CD8+ T-cell maintenance and subsequent viral control.

METHODS

We compared levels of IL-21R expression on total and memory subsets of CD8+ T cells from HIV-1-negative and HIV-1-positive donors. We also measured IL-21R on antigen-specific CD8+ T cells in volunteers who were positive for HIV-1 and had cytomegalovirus-responding T cells. Finally, we quantified plasma IL-21 in treatment-naive HIV-1-positive individuals and compared this with IL-21R expression.

RESULTS

IL-21R expression was significantly higher on CD8+ T cells (P = 0.0256), and on central memory (P = 0.0055) and effector memory (P = 0.0487) CD8+ T-cell subsets from HIV-1-positive individuals relative to HIV-1-negative individuals. For those infected with HIV-1, the levels of IL-21R expression on HIV-1-specific CD8+ T cells correlated significantly with visit viral load (r = 0.6667, P = 0.0152, n = 13) and inversely correlated with plasma IL-21 (r = -0.6273, P = 0.0440, n = 11). Lastly, CD8+ T cells from individuals with lower set point viral load who demonstrated better viral control had the lowest levels of IL-21R expression and highest levels of plasma IL-21.

CONCLUSION

Our data demonstrates significant associations between IL-21R expression on peripheral CD8+ T cells and viral load, as well as disease trajectory. This suggests that the IL-21 receptor could be a novel marker of CD8+ T-cell dysfunction during HIV-1 infection.

Reversing T-cell exhaustion in immunotherapy: a review on current approaches and limitations

Introduction:T cell functions are altered during chronic viral infections and tumor development. This is mainly manifested by significant changes in T cells' epigenetic and metabolic landscapes, pushing them into an 'exhausted' state. Reversing this T cell exhaustion has been emerging as a 'game-changing' therapeutic approach against cancer and chronic viral infection.Areas covered:This review discusses the cellular pathways related to T cell exhaustion, and the clinical development and possible cellular targets that can be exploited therapeutically to reverse this exhaustion. We searched various databases (e.g. Google Scholar, PubMed, Elsevier, and other scientific database sites) using the keywords T cell exhaustion, T cell activation, co-inhibitory receptors, and reversing T cell exhaustion.Expert opinion:The discovery of the immune checkpoints pathways represents a significant milestone toward understanding and reversing T cell exhaustion. Antibodies that target these pathways have already demonstrated promising activities in reversing T cell exhaustion. Nevertheless, there are still many associated limitations. In this context, next-generation alternatives are on the horizon. This includes the use of small molecules to block the immune checkpoints' receptors, combining them with other treatments, and identifying novel, safer and more effective immunotherapeutic targets.

Follicular helper-T cells restore CD8+-dependent antitumor immunity and anti-PD-L1/PD-1 efficacy

Background

T follicular helper cells (Tfh) are essential to shape B cell response during germinal center formation. Tfh accumulation has been reported in various human cancers, with positive or negative prognostic roles. However, the mechanisms explaining the accumulation of Tfh and their role in cancer remain obscure.

Methods

In vitro differentiated and mouse cell sorted Tfh phenotype was evaluated by flow cytometry and quantitative PCR (qPCR). Antitumor effect of Tfh was evaluated by adoptive transfer in different tumor-bearing mice models. The involvement of immune cells, cytokines and chemokines was evaluated, using depleting antibodies. Chemokines and cytokines expression and production were evaluated by qPCR and ELISA. In human, the impact of immune cells and chemokines on survival was evaluated by analyzing transcriptomic data from public databases and from our own patient cohorts.

Results

In this study, we show that Tfh exert an antitumor immune effect in a CD8⁺-dependent manner. Tfh produce interleukin-21, which sustains proliferation, viability, cytokine production and cytotoxic functions of exhausted T cells. The presence of Tfh is required for efficacy of antiprogrammed cell death ligand-1 therapy. Tfh accumulate in the tumor bed and draining lymph nodes in different mouse cancer models. This recruitment is due to the capacity of transforming growth factor β to drive Chemokine (C-X-C motif) Ligand 13 expression, a chemoattractant of Tfh, by intratumor CD8⁺ T cells. Accumulation of Tfh and exhausted CD8⁺ T cells predicts cancer outcome in various cancer types. In patients treated with anti-programmed cell death-1 mAb, accumulation of Tfh and CD8⁺ at the tumor site is associated with outcome.

Conclusion

This study provides evidence that CD8⁺/Tfh crosstalk is important in shaping antitumor immune response generated by immunotherapy.

Lipophagy confers a key metabolic advantage that ensures protective CD8A T-cell responses against HIV-1

Although macroautophagy/autophagy has been proposed as a critical defense mechanism against HIV-1 by targeting viral components for degradation, its contribution as a catabolic process in providing optimal anti-HIV-1 immunity has never been addressed. The failure to restore proper antiviral CD8A/CD8 T-cell immunity, especially against HIV-1, is still the major limitation of current antiretroviral therapies. Consequently, it is of clinical imperative to provide new strategies to enhance the function of HIV-1-specific CD8A T-cells in patients under antiretroviral treatments (ART). Here, we investigated whether targeting autophagy activity could be an optional solution to make this possible. Our data show that, after both polyclonal and HIV-1-specific activation, CD8A T-cells from ART displayed reduced autophagy-dependent degradation of lysosomal contents when compared to naturally HIV-1 protected elite controllers (EC). We further confirmed in EC, by using specific BECN1 gene silencing and lysosomal inhibitors, the critical role of active autophagy in superior CD8A T-cell protection against HIV-1. More importantly, we found that an IL21 treatment was effective in rescuing the antiviral CD8A T-cell immunity from ART in an autophagy-dependent manner. Finally, we established that IL21-dependent rescue occurred due to the enhanced degradation of endogenous lipids via autophagy, referred to as lipophagy, which fueled the cellular rates of mitochondrial beta-oxidation. In summary, our data show that autophagy/lipophagy can be considered as a therapeutic tool to elicit functional antiviral CD8 T-cell responses. Our results also provide additional insights toward the development of improved T-cell-based prevention and cure strategies against HIV-1.Abbreviations: ART: patients under antiretroviral therapy; BaF: bafilomycin A₁; BECN1: beclin 1; CEF: cytomegalo-, Epstein-Barr- and flu-virus peptide pool; Chloro.: chloroquine; EC: elite controllers; FAO: fatty acid beta-oxidation; HIV^neg: HIV-1-uninfected control donors; IFNG/IFN-γ: interferon gamma; IL21: interleukin 21; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; PBMC: peripheral blood mononuclear cells; SQSTM1: sequestosome 1; ULK1: unc-51 like autophagy activating kinase 1.

Insight in miRNome of Long-Term Non-Progressors and Elite Controllers Exposes Potential RNAi Role in Restraining HIV-1 Infection

Long-term non-progressors (LTNP) and elite controllers (EC) represent spontaneous natural models of efficient HIV-1 response in the absence of treatment. The main purposes of this work are to describe the miRNome of HIV-1 infected patients with different extreme phenotypes and identify potentially altered pathways regulated by differentially expressed (DE) miRNAs. The miRNomes from peripheral blood mononuclear cells (PBMCs) of dual phenotype EC-LTNP or LTNP with detectable viremia and HIV-infected patients with typical progression before and after treatment, were obtained through miRNA-Seq and compared among them. The administration of treatment produces 18 DE miRNAs in typical progressors. LTNP condition shows 14 DE miRNA when compared to typical progressors, allowing LTNP phenotype differentiation. A set of four miRNAs: miR-144-3p, miR-18a-5p, miR-451a, and miR-324 is strongly downregulated in LTNP and related to protein regulation as AKT, mTOR, ERK or IKK, involved in immune response pathways. Deregulation of 28 miRNA is observed between EC-LTNP and viremic-LTNP, including previously described anti-HIV miRNAs: miR-29a, associated with LTNP phenotype, and miR-155, targeting different pre-integration complexes such as ADAM10 and TNPO3. A holistic perspective of the changes observed in the miRNome of patients with different phenotypes of HIV-control and non-progression is provided.

Safety and Immunological Evaluation of Interleukin-21 Plus Anti-α4β7 mAb Combination Therapy in Rhesus Macaques

Human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) infections compromise gut immunological barriers, inducing high levels of inflammation and a severe depletion of intestinal CD4+ T cells. Expression of α4β7 integrin promotes homing of activated T cells to intestinal sites where they become preferentially infected; blockade of α4β7 with an anti-α4β7 monoclonal antibody (mAb) prior to infection has been reported to reduce gut SIV viremia in rhesus macaques (RMs). Interleukin-21 (IL-21) administration in antiretroviral therapy-treated, SIV-infected RMs reduces gut inflammation and improves gut integrity. We therefore hypothesized that the combination of IL-21 and anti-α4β7 mAb therapies could synergize to reduce inflammation and HIV persistence. We co-administered two intravenous doses of rhesus anti-α4β7 mAb (50 mg/kg) combined with seven weekly subcutaneous infusions of IL-21-IgFc (100 μg/kg) in four healthy, SIV-uninfected RMs to evaluate the safety and immunological profiles of this intervention in blood and gut. Co-administration of IL-21 and anti-α4β7 mAb showed no toxicity at the given dosages as assessed by multiple hematological and chemical parameters and did not alter the bioavailability of the therapeutics or result in the generation of antibodies against the anti-α4β7 mAb or IL-21-IgFc. Upon treatment, the frequency of CD4 memory T cells expressing β7 increased in blood and decreased in gut, consistent with an inhibition of activated CD4 T-cell homing to the gut. Furthermore, the frequency of T cells expressing proliferation and immune activation markers decreased in blood and, more profoundly, in gut. The combined IL-21 plus anti-α4β7 mAb therapy is well-tolerated in SIV-uninfected RMs and reduces the gut homing of α4β7+ CD4 T cells as well as the levels of gut immune activation.

Persistent expansion and Th1-like skewing of HIV-specific circulating T follicular helper cells during antiretroviral therapy

Background

Untreated HIV infection leads to alterations in HIV-specific CD4⁺ T cells including increased expression of co-inhibitory receptors (IRs) and skewing toward a T follicular helper cell (Tfh) signature. However, which changes are maintained after suppression of viral replication with antiretroviral therapy (ART) is poorly known.

Methods

We analyzed blood CD4⁺ T cells specific to HIV and comparative viral antigens in ART-treated people using a cytokine-independent activation-induced marker assay alone or in combination with functional readouts.

Findings

In intra-individual comparisons, HIV-specific CD4⁺ T cells were characterized by a larger fraction of circulating Tfh (cTfh) cells than CMV- and HBV-specific cells and preferentially expressed multiple IRs and showed elevated production of the Tfh cytokines CXCL13 and IL-21. In addition, HIV-specific cTfh exhibited a predominant Th1-like phenotype and function when compared to cTfh of other specificities, contrasting with a reduction in Th1-functions in HIV-specific non-cTfh. Using longitudinal samples, we demonstrate that this distinct HIV-specific cTfh profile was induced during chronic untreated HIV infection, persisted on ART and correlated with the translation-competent HIV reservoir but not with the total HIV DNA reservoir.

Interpretation

Expansion and altered features of HIV-specific cTfh cells are maintained during ART and may be driven by persistent HIV antigen expression.

Funding

This work was supported by the National Institutes of Health (NIH), the Canadian Institutes of Health Research (CIHR) and the FRQS AIDS and Infectious Diseases Network.

Japanese flounder Paralichthys olivaceus interleukin 21 induces inflammatory response and plays a vital role in the immune defense against bacterial pathogen

Interleukin (IL)-21 is a pleiotropic cytokine and plays a vital role in immunity. In the current study, we examined the immune function of Japanese flounder Paralichthys olivaceus IL-21 (PoIL-21). PoIL-21 shares moderate (25.17%-46.25%) sequence identities with other teleost IL-21. PoIL-21 expression occurred in multiple tissues, especially intestine, and was regulated by bacterial infection in a time dependent manner. PoIL-21 was secreted by peripheral blood leukocytes (PBL) upon LPS stimulation. Recombinant PoIL-21 (rPoIL-21) bound to a wide range of Gram-negative and Gram-positive bacteria and inhibited the growth of the fish bacterial pathogen Streptococcus iniae. rPoIL-21 also interacted with PBL, resulting in enhanced cell proliferation, ROS production, and expression of IL-1β, TNF-α, CD8β, T-bet, PoIL-21, PoIL-21 receptor, and STAT. Consequently, the presence of rPoIL-21 significantly reduced bacterial infection in PBL. In vivo study showed that rPoIL-21 upregulated the expression of inflammatory cytokines and PoIL-21. Taken together, these results indicate that PoIL-21 is an inducible, secreted cytokine with a broad range of binding capacities and plays an important role in the regulation of anti-bacterial immunity.

IL-21 is associated with natural resistance to HIV-1 infection in a Colombian HIV exposed seronegative cohort

Higher IL-21 levels were associated with natural resistance to HIV infection in an Italian cohort. Thus we wanted to confirm such association in HIV exposed seronegative individuals (HESN) from Colombia. Cells from HESN were less susceptible to infection and expressed higher IL-21 mRNA levels than healthy controls at both baseline and 7-days post-infection; similar results were observed for IL-6, perforin, and granzyme. These results suggest that IL-21/IL-6 increase may be a distinctive quality in the profile of HIV-1 resistance, at least during sexual exposure. However, further studies are necessary to confirm the specific protective mechanisms of these cytokines.

Interleukin 21 Reinvigorates the Antiviral Activity of Hepatitis B Virus (HBV)-Specific CD8+ T Cells in Chronic HBV Infection

BACKGROUND

Strategies that target functional recovery of exhausted hepatitis B virus (HBV)-specific CD8+ T cells are beneficial for viral control, but the potential for interleukin 21 (IL-21) to rescue CD8+ T-cell function is not well understood.

METHODS

We investigated the effect of IL-21 on CD8+ T-cell responses by phenotypic and functional analysis of samples from patients with chronic HBV infection and a mouse model with HBV expression.

RESULTS

IL-21 promoted the proliferative capacity of HBV-specific CD8+ T cells and down-regulated expression of the inhibitory receptors programmed death 1 and T-cell immunoglobulin domain and mucin domain 3. Additionally, IL-21 boosted the production of interferon-γ, granzyme B, and CD107a in HBV-specific CD8+ T cells and enhanced the cytolytic activity of CD8+ T cells against HepG2.2.15 cells. Notably, an HBV mouse model established from IL-21 receptor knockout mice showed significantly decreased frequency of HBV-specific CD8+ T cells and increased levels of serum hepatitis B surface antigen (HBsAg). Meanwhile, administration of recombinant mouse IL-21 in an HBV mouse model established from wild-type mice resulted in enhanced functionality of HBV-specific CD8+ T cells and accelerated HBsAg clearance.

CONCLUSIONS

IL-21 enhances the antiviral effect of HBV-specific CD8+ T cells, suggesting that it may contribute to viral clearance in chronic HBV infection.

The anti-inflammatory IL-37/SIGIRR axis is functionally compromised in HIV infection

BACKGROUND

IL-37 is a member of the IL-1 family with potent anti-inflammatory effects. Little is known about regulation of the cytokine and of its signaling co-receptor SIGIRR in HIV infection.

OBJECTIVES

Our main objective was to investigate how production of the cytokine and expression of SIGIRR on immune cells is regulated in HIV infection.

METHODS

The study was conducted using biological samples from a cross section of HIV-infected individuals. Concentrations of IL-37, TNF-α and soluble form of SIGIRR in serum samples were determined by ELISA. The expression of SIGIRR on immune cells was determined by flow cytometry. IL-37 isoform-specific transcripts were determined in PBMC by RT-PCR using isoform-specific primers. The effects of exogenous IL-37 on HIV replication in human phytohaemagglutinin (PHA) blasts were determined in in-vitro assays.

RESULTS

The cytokine concentrations tended to decrease in treatment-naive HIV-infected individuals. They were higher in treated HIV-infected individuals compared with those from treatment-naive ones. Higher concentrations of the cytokine were observed in sera from LTNP. The expression of SIGIRR on immune cells was decreased in HIV-infected individuals. On the other hand, its soluble form increased in the sera in these individuals. The trend was reversed in the patients undergoing antiretroviral treatment. Soluble SIGIRR attenuated anti-inflammatory effects of the cytokine. Serum IL-37 and soluble SIGIRR concentrations correlated with certain clinical parameters of the patients. Furthermore, recombinant human IL-37 inhibited HIV replication in human PHA blasts.

CONCLUSION

The IL-37/SIGIRR axis is functionally compromised in HIV-infected individuals. Targeting the axis may alleviate inflammation and decrease HIV replication in this viral infection.

IL-27 in patients with Chikungunya fever: A possible chronicity biomarker?

BACKGROUND/PURPOSE

Although many patients with chikungunya virus disease (CHIKVD), an arboviral disease characterized by sudden fever and incapacitating poliartralgia, develop chronic articular symptoms, the mechanisms involved in CHIKVD's chronification and its possible biomarkers remain poorly understood. Interleukin (IL)-17A, IL-21, IL-22, IL-29, and transforming growth factor (TGF)-β have been implicated in the pathogenesis of other inflammatory joint diseases, including rheumatoid arthritis, psoriatic arthritis, and ankylosing spondylitis. Since chronic manifestations of CHIKVD share many clinical and immunological characteristics with those diseases, we assessed the serum levels of those cytokines and analyzed their associations with clinical manifestations in patients with CHIKVD.

METHODS

We evaluated 45 patients (36 female, mean age: 55.2 ± 13.8 years) with CHIKVD serologically confirmed by enzyme-linked immunosorbent assay (ELISA), articular manifestations upon evaluation, and no previous history of inflammatory rheumatologic diseases, along with 49 healthy age- and sex-matched controls. We tested anti-Chikungunya IgM and IgG antibodies and measured IL-17A, IL-21, IL-22, IL-27, IL-29, and TGF-β serum levels with specific ELISA kits.

RESULTS

IL-27, IL-17A, and IL-29 appeared in most patients but not in controls. IL-27 serum levels were higher in patients with chronic symptoms (median: 523.0 pg/mL [62.5-1,048]) than in ones in the acute or subacute stage (median: 62.5 pg/mL [62.5-483.8], p = .008). In patients with CHIKVD, we found significant correlations between IL-27 levels and tender joint counts (r = .32, p = .006), along with associations between IL-17A levels and swollen joint counts (r = .315, p = .0352). Furthermore, patients with arthritis had higher IL-17A levels (median: 23.14 pg/mL [20.6-25.86]) than ones without (median: 20.29 pg/mL [3.91-22.43], p = .0352). We did not detect IL-22 in either group or IL-21 in patients with CHIKVD.

CONCLUSION

Serum levels of IL-17A, IL-27, and IL-29 were high in patients with CHIKVD and had important associations with articular manifestations, which might indicate the inflammatory nature of Chikungunya infection in patients with joint symptoms and the roles of those cytokines in the disease's pathophysiology.

Interleukin-21 Regulates Natural Killer Cell Responses During Mycobacterium tuberculosis Infection

Background

In the current study, we determined the effects of interleukin (IL)-21 on human natural killer (NK) cells and monocyte responses during Mycobacterium tuberculosis (Mtb) infection.

Methods

We found that Mtb stimulated CD4+ and NK T cells from healthy individuals with latent tuberculosis infection (LTBI+) are major sources of IL-21. CD4+ cells from tuberculosis patients secreted less IL-21 than did CD4+ cells from healthy LTBI+ individuals. Interleukin-21 had no direct effect on Mtb-stimulated monocytes.

Results

Interleukin-21-activated NK cells produced interferon (IFN)-γ, perforin, granzyme B, and granulysin; lysed Mtb-infected monocytes; and reduced Mtb growth. Interleukin-21-activated NK cells also enhanced IL-1β, IL-18, and CCL4/macrophage-inflammatory protein (MIP)-1β production and reduced IL-10 production by Mtb-stimulated monocytes. Recombinant IL-21 (1) inhibited Mtb growth, (2) enhanced IFN-γ, IL-1β, IL-18, and MIP-1β, and (3) reduced IL-10 expression in the lungs of Mtb-infected Rag2 knockout mice.

Conclusions

These findings suggest that activated T cells enhance NK cell responses to lyse Mtb-infected human monocytes and restrict Mtb growth in monocytes through IL-21 production. Interleukin-21-activated NK cells also enhance the immune response by augmenting IL-1β, IL-18, and MIP-1β production and reducing IL-10 production by monocytes in response to an intracellular pathogen.

Mucosal T follicular helper cells in SIV-infected rhesus macaques: contributing role of IL-27

Mesenteric lymph nodes (MLNs), that drain the large and small intestine, are critical sites for the induction of oral tolerance. Although depletion of CD4 T cells in the intestinal lamina propria is a hallmark of HIV infection, CD4 T cell dynamics in MLNs is less known due to the lack of accessibility to these LNs. We demonstrate the early loss of memory CD4 T cells, including T follicular helper cells (Tfh) and a remodeling of MLN architecture in SIV-infected rhesus macaques (RMs). Along with the loss of Tfh cells, we observe the loss of memory B cells and of germinal center B cells. Tfh cells display a Th1 profile with increased levels of the transcription factors that negatively impact on Tfh differentiation and of Stat5 phosphorylation. MLNs of SIV-infected RMs display lower mRNA transcripts encoding for IL-12, IL-23, and IL-35, whereas those coding for IL-27 are not impaired in MLNs. In vitro, IL-27 negatively impacts on Tfh cells and recapitulates the profile observed in SIV-infected RMs. Therefore, early defects of memory CD4 T cells, as well of Tfh cells in MLNs, which play a central role in regulating the mucosal immune response, may have major implications for Aids.

Interleukin 21 (IL-21)/microRNA-29 (miR-29) axis is associated with natural resistance to HIV-1 infection

BACKGROUND

Interleukin-21 (IL-21) modulates HIV-1 infection through the elicitation of different antiviral mechanisms, including Th17 lineage commitment and induction of microRNA (miR)-29, a miRNA endowed with anti-HIV activity. As miR-29 expression is significantly increased in HIV-1-exposed seronegative individuals (HESN), we investigated the role of miR-29/IL21 axis in the natural control of HIV-1 infection.

METHODS

Peripheral blood mononuclear cells (PBMCs) isolated from 15 Italian sexually exposed HESN and 15 HIV-unexposed healthy controls were in-vitro infected with an R5-tropic HIV-1Ba-L strain. Seven days post HIV-1 infection we evaluated: 1) p24 production (ELISA); 2) CD4/IL-21 and CD4/IL-17 T lymphocytes (FACS); 3) IL-17 concentration in supernatants (ELISA); and 4) IL-6, IL-17, IL-21, and miR-29a,b,c expression by CD4 T lymphocytes as well as perforin and granzyme by peripheral blood mononuclear cells (qPCR). The same analyses were performed on the 15 HIV-positive partners.

RESULTS

At baseline IL-6 expression alone was increased in HESN compared to healthy controls. Seven days after in-vitro HIV-1 infection, nevertheless, differences emerged. Thus, CD4/IL21 and CD4/IL17 T lymphocytes, as well as IL-21 and IL-17 expression and production were significantly augmented in HESN compared to healthy controls. Interestingly, IL-21 upregulation correlated with a significantly increased expression of miR-29a,b,c and a reduced susceptibility to in-vitro HIV-1 infection in HESN alone. No differences were observed in perforin and granzyme expression.

CONCLUSION

The IL-21/miR-29 axis is upregulated by HIV-1 infection in HESN suggesting its involvement in the natural resistance to HIV-1 infection in HESN. Approaches that exogenously increase IL-21 production or prompt preexisting cellular IL-21 reservoir could confine the magnitude of the initial HIV-1 infection.

Kinetics of Interferon gamma and Interleukin-21 response following foot and mouth disease virus infection

Foot and mouth disease (FMD) is one of the most contagious diseases of cloven footed animals causing significant economic impediment in livestock production system. The immune response to FMD virus (FMDV) infection is regulated by a complex interplay between various cells, cytokines and other immune components. Based on the well established role of Interferon-gamma (IFN-γ) and Interleukin-21 (IL-21) in viral infections, this study aimed to determine expression level of these cytokines in clinically infected adults and calves; and the results were compared with those in the subclinically infected animals up to 120 days post outbreak (DPO) in a vaccinated cattle herd. The expression level of IFN-γ and IL-21 was assayed on 0, 7, 14, 28, 60, 90, and 120 DPO by enzyme linked immunosorbent assay (ELISA) with simultaneous assessment of FMDV structural protein-antibody titer against serotype 'O' by liquid phase blocking ELISA (LPBE) and nonstructural protein-antibody, a differential marker of infection, using r3AB3 indirect ELISA (r3AB3 I-ELISA). Although, the peak expression of IFN-γ was observed on 14 DPO across all categories of animals, the clinically infected animals registered a significant increase in IFN-γ level as compared to the subclinically infected population possibly due to the difference in the extent of virus replication and inflammation. The IL-21 level increased significantly during 14-28 DPO and highest expression was noticed on 28 DPO. The increase in the expression level of IFN-γ and IL-21 at 28 DPO correlated with the increase in antibody titer as determined by LPBE suggesting the role of these cytokines in augmenting immune response to FMDV infection.

Differentiation and Function of Follicular CD8 T Cells During Human Immunodeficiency Virus Infection

The combination antiretroviral therapeutic (cART) regime effectively suppresses human immunodeficiency virus (HIV) replication and prevents progression to acquired immunodeficiency diseases. However, cART is not a cure, and viral rebound will occur immediately after treatment is interrupted largely due to the long-term presence of an HIV reservoir that is composed of latently infected target cells that maintain a quiescent state or persistently produce infectious viruses. CD4 T cells that reside in B-cell follicles within lymphoid tissues, called follicular helper T cells (TFH), have been identified as a major HIV reservoir. Due to their specialized anatomical structure, HIV-specific CD8 T cells are largely insulated from this TFH reservoir. It is increasingly clear that the elimination of TFH reservoirs is a key step toward a functional cure for HIV infection. Recently, several studies have suggested that a fraction of HIV-specific CD8 T cells can differentiate into a CXCR5-expressing subset, which are able to migrate into B-cell follicles and inhibit viral replication. In this review, we discuss the differentiation and functions of this newly identified CD8 T-cell subset and propose potential strategies for purging TFH HIV reservoirs by utilizing this unique population.

Deciphering natural control of HIV-1: A valuable strategy to achieve antiretroviral therapy termination

Antiretroviral therapy (ART) has dramatically reduced HIV-1-associated morbidity and mortality, and has transformed HIV-1 infection into a manageable chronic condition by suppressing viral replication. However, despite recent patient care improvements, ART still fails to cure HIV-1 infection due to the inability to counteract immune defects and metabolic disturbances that are associated with residual inflammation alongside viral persistence. Life-long drug administration also results in multiple side-effects in patients including lipodystrophy and insulin resistance. Thus, it is critical to find new ways to reduce the length of treatment and facilitate the termination of ART, for example by boosting protective immunity. The rare ability of some individuals to naturally control HIV-1 infection despite residual inflammation could be exploited to identify molecular mechanisms involved in host protection that may function as potential therapeutic targets. In this review, we highlight evidence illustrating the molecular and metabolic advantages of HIV-1 controllers over ART treated patients that contribute to the maintenance of effective antiviral immunity.

IL-21 as a Predictor of Sustained Virologic Response in Patients with Chronic Hepatitis C Virus Infection

Hepatitis C virus (HCV) infection is a significant public health problem. The crucial role of interleukin (IL)-21 in HCV has been established. Thus, we aimed to investigate the association of serum IL-21 levels with the virological response to interferon (IFN)-based therapy in a group of Egyptian patients with chronic hepatitis C (CHC). Clinical data were collected from 58 HCV-positive Egyptian patients treated with IFN/ribavirin therapy and 10 non-HCV-infected healthy subjects. Liver and renal function tests, complete blood count, viral markers, and pretreatment IL-21 levels were determined in all patients and healthy controls. Patients who achieved sustained virologic response (SVR) had higher pretreatment median serum IL-21 levels than those who did not. Thus, this study concluded that higher pretreatment serum IL-21 may be useful in predicting SVR in CHC patients.

Up-regulation of Interleukin-21 Contributes to Liver Pathology of Schistosomiasis by Driving GC Immune Responses and Activating HSCs in Mice

The pathology of schistosome egg-induced liver granuloma, fibrosis and eventually liver scarring is complicated. CD4⁺ helper T (Th) cells play critical roles in both host humoral immunity and cellular immunity against parasitic infection and immunopathology in schistosomiasis. Follicular helper T (Tfh) cells are another specialized subset of Th cells and involved in infectious diseases. However, the immune regulatory mechanism of Tfh cells in severe liver pathology of schistosomiasis is still poorly understood. In this study, using a S. japonicum-infected mouse model, we studied the dynamics and effects of Tfh cells in vivo and demonstrated that Tfh phenotype molecules ICOS, PD-1 and functional factor IL-21 were positively correlated with disease development by flow cytometry. Meanwhile, our results also showed that Tfh cells enriched in splenic germinal center (GC) and promoted B cells producing IgM with the progress of hepatic immunopathology by B-T co-culture experiments. More importantly, our data indicated that IL-21 contributed to the formation and development of hepatic egg granuloma and subsequent fibrosis by driving GC responses and activating HSCs by immunohistochemical detection and blocking assay in vitro. Our findings contribute to the better understanding of the immunopathogenesis of schistosomiasis and have implications for therapeutic intervention of hepatic fibrotic diseases.

IL-21 Therapy Controls Immune Activation and Maintains Antiviral CD8+ T Cell Responses in Acute Simian Immunodeficiency Virus Infection

Human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) replicate during acute infection in lymphocytes of the gastrointestinal tract, before disseminating systemically. Localized replication and associated loss of gut-resident CD4⁺ T cells occur regardless of the portal of entry of the virus (e.g., intravenous vs. rectal). Thus, HIV and SIV are tropic for gut tissue, and their pathogenesis requires the special environment of the intestine. T helper 17 (Th17) cells are important contributors to microbial defense in the gut that are vulnerable to HIV infection and whose loss is associated with translocation of microbial products to the systemic circulation, leading to chronic immune activation and disease progression. Interleukin (IL)-21 promotes differentiation and survival of Th17 cells and stimulates CD8⁺ T cell function. By promoting Th17 cell survival, IL-21 could limit bacterial translocation and immune activation in the setting of acute or rebounding HIV/SIV disease. In this study, we tested the effect of recombinant IL-21-IgFc treatment, given at the time of infection, on SIV_mac251 infection. We found that rIL-21-IgFc decreases immune activation and maintains effective antiviral responses by CD8⁺ T cells in blood, but this maintenance is not associated with lower viral loads. rIL-21-IgFc treatment also did not generally support Th17 cell populations, but Th17 cells remained strongly and independently associated with control of plasma viremia. For example, the single animal exhibiting greatest control over viremia in our study also manifested the highest levels of IL-21 in plasma, Th17 cell maintenance in blood, and Th17 cells in intestinal tissue. These findings provide rationale for further exploration of IL-21 treatment as a support for host CD8⁺ T cell responses in HIV cure strategies.

Designing optimal HIV-vaccine T-cell responses

PURPOSE OF REVIEW

T cells can efficaciously control HIV replication, and it has been hypothesized that inducing those responses before exposure occurs may prevent HIV infection. However, conventional attempts to generate protective CD8 T-cell responses against HIV have generally failed. Based on current knowledge from chronic HIV infection and previous vaccine trials, this review details optimal CD8 and CD4 T-cell response design that may confer protection from HIV infection.

RECENT FINDINGS

The failure of two vaccines geared toward inducing T-cell response (STEP trial and HVTN505/Phambili) as well as the modest protection of the RV144 that mainly demonstrated nonneutralizing antibodies to be a correlate of protection have rattled the idea that a pure T-cell-based vaccine may induce protection. Moreover, in the recent years, CD4 T cells, and in particular the T follicular helper cell subset, received attention as a critical component for T-cell-inducing and antibody-inducing vaccines.

SUMMARY

It is apparent that all vaccines depend for their efficacy on a cellular component either to directly kill virally infected cells or to provide important helper signals for the development of efficacious B-cell responses. Recent vaccine trials have had a major impact on the field and are guiding new approaches for HIV vaccine design.

The loss of CCR6+ and CD161+ CD4+ T-cell homeostasis contributes to disease progression in SIV-infected rhesus macaques

Although previous studies have shown that CD4+ T cells expressing CCR6 and CD161 are depleted from blood during HIV infection, the mechanisms underlying their loss remain unclear. In this study, we investigated how the homeostasis of CCR6+ and CD161+ CD4+ T cells contributes to SIV disease progression and the mechanisms responsible for their loss from circulation. By comparing SIV infection in rhesus macaques (RMs) and natural host sooty mangabeys (SMs), we found that the loss of CCR6+ and CD161+ CD4+ T cells from circulation is a distinguishing feature of progressive SIV infection in RMs. Furthermore, while viral infection critically contributes to the loss of CD161+CCR6-CD4+ T cells, a redistribution of CCR6+CD161- and CCR6+CD161+CD4+ T cells from the blood to the rectal mucosa is a chief mechanism for their loss during SIV infection. Finally, we provide evidence that the accumulation of CCR6+CD4+ T cells in the mucosa is damaging to the host by demonstrating their reduction from this site following initiation of antiretroviral therapy in SIV-infected RMs and their lack of accumulation in SIV-infected SMs. These data emphasize the importance of maintaining CCR6+ and CD161+ CD4+ T-cell homeostasis, particularly in the mucosa, to prevent disease progression during pathogenic HIV/SIV infection.

Diminished plasma levels of common γ-chain cytokines in pulmonary tuberculosis and reversal following treatment

Background

The immune response to tuberculosis (TB) is T cell dependent. T cells are the major facilitators of protection and effector functions with CD4⁺ T cells being the most important players, followed by CD8⁺ T cells. The common γ-chain cytokines IL-2, IL-7, IL-15, and IL-21 play a vital role in peripheral T cell growth and survival. However, the role of common γ-chain cytokines in pulmonary TB (PTB) is poorly understood.

Aim and methods

To examine the association of circulating common γ-chain cytokines with TB disease or infection, we examined the systemic levels of IL-2, IL-7, IL-15, and IL-21 in individuals with PTB, latent TB (LTB) or no TB infection (NTB). We also examined the levels of these cytokines in PTB individuals before and after anti-tuberculosis treatment.

Results

Circulating levels of IL-2, IL-7 and IL-21 were significantly diminished in PTB compared to LTB or NTB individuals. Moreover, TB antigen stimulated whole blood also exhibited diminished levels of common γ-chain cytokines in PTB compared to LTB or NTB individuals. The plasma levels of common γ-chain cytokines exhibited no significant association with the severity or extent of TB disease or with bacterial burdens. However, upon standard anti-TB treatment, both the systemic as well as the TB antigen stimulated levels of IL-2, IL-7 and IL-21 were significantly increased in PTB individuals.

Conclusion

Therefore our data demonstrate that diminished levels of common γ-chain cytokines are a common characteristic of PTB and potentially highlight the importance of boosting these responses to improve treatment outcomes.

Role of IL-21 in HTLV-1 infections with emphasis on HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP)

Interleukin-21 (IL-21) enhances the survival and cytotoxic properties of cytotoxic T cells (CTLs) and exhibits essential roles in controlling chronic viral infections. HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) is a chronic progressive inflammatory disease of the nervous system. The main determinant of disease progression is efficiency of the CTL response to Human T lymphotropic virus types I (HTLV-1). In this study, the expression of host IL-21 and HTLV-I Tax and proviral load (PVL) was evaluated to understand the role and mechanism of IL-21 in HTLV-1 infections and the subsequent development of HAM/TSP. A cross-sectional study was carried out on 20 HAM/TSP patients, 20 asymptomatic HTLV-1 carriers (ACs) and 20 healthy controls (HCs) to evaluate the expression of IL-21 and Tax and PVL in non-activated and phorbol myristate acetate (PMA)-ionomycin-activated peripheral blood mononuclear cells (PBMCs). The mean mRNA expression of IL-21 in the non-activated and activated PBMCs was higher (by 5-13 times) in the HAM/TSP patients than in ACs and HCs (p < 0.05); however, there was no significant difference between ACs and HCs. In contrast to the IL-21 mRNA expression, the serum level of the IL-21 protein was significantly lower in the HAM/TSP patients than in ACs and HCs (p < 0.05). Furthermore, higher expression of Tax and PVL was observed in the HAM/TSP subjects than ACs (p < 0.05). In addition, Tax gene expression was positively correlated with PVL (R = 0.595, p = 0.000) and IL-21 gene expression (R = 0.395, p = 0.021) in the HTLV-1-infected subjects. In conclusion, the increase in IL-21 mRNA expression may reflect the attempt of infected T cells to induce an appropriate antiviral response, and the decrease in IL-21 protein expression may reflect the inhibition of IL-21 mRNA translation by viral factors in favour of virus evasion and dissemination.

CD4 T Follicular Helper Cells and HIV Infection: Friends or Enemies?

Follicular T helper (Tfh) cells, a subset of CD4 T lymphocytes, are essential for memory B cell activation, survival, and differentiation and assist B cells in the production of antigen-specific antibodies. Work performed in recent years pointed out the importance of Tfh cells in the context of HIV and SIV infections. The importance of tissue distribution of Tfh is also an important point since their frequency differs between peripheral blood and lymph nodes compared to the spleen, the primary organ for B cell activation, and differentiation. Our recent observations indicated an early and profound loss of splenic Tfh cells. The role of transcriptional activator and repressor factors that control Tfh differentiation is also discussed in the context of HIV/SIV infection. Because Tfh cells are important for B cell differentiation and antibody production, accelerating the Tfh responses early during HIV/SIV infection could be promising as novel immunotherapeutic approach or alternative vaccine strategies. However, because Tfh cells are infected during the HIV/SIV infection and represent a reservoir, this may interfere with HIV vaccine strategy. Thus, Tfh represent the good and bad guys during HIV infection.

B10 Cell Frequencies and Suppressive Capacity in Myasthenia Gravis Are Associated with Disease Severity

Myasthenia gravis (MG) is a T cell-dependent, B cell-mediated disease. The mechanisms for loss of self-tolerance in this disease are not well understood, and recently described regulatory B cell (Breg) subsets have not been thoroughly investigated. B10 cells are a subset of Bregs identified by the production of the immunosuppressive cytokine, interleukin-10 (IL-10). B10 cells are known to strongly inhibit B- and T-cell inflammatory responses in animal models and are implicated in human autoimmunity. In this study, we examined quantitative and qualitative aspects of B10 cells in acetylcholine receptor autoantibody positive MG (AChR-MG) patients and healthy controls. We observed reduced B10 cell frequencies in AChR-MG patients, which inversely correlated with disease severity. Disease severity also affected the function of B10 cells, as B10 cells in the moderate/severe group of MG patients were less effective in suppressing CD4 T-cell proliferation. These results suggest that B10 cell frequencies may be a useful biomarker of disease severity, and therapeutics designed to restore B10 cell frequencies could hold promise as a treatment for this disease through restoration of self-tolerance.

CD4+IL-21+T cells are correlated with regulatory T cells and IL-21 promotes regulatory T cells survival during HIV infection

INTRODUCTION

IL-21 enhances T and natural killer cells survival and antiviral functions without promoting T cell activation during HIV infection, which makes it a better adjuvant in anti-HIV immunotherapy. Due to the pleiotropy and redundancy of cytokines, it is vital to have a comprehensive knowledge of the role of IL-21 in the regulation of immune responses. Regulatory T cells (Tregs) play an important role in immune regulation and are a determinant of immune therapeutic efficacy in certain circumstances. In this study, we explored the direct effect of IL-21 on Tregs during HIV infection, which has not been addressed before.

METHODS

Thirty-four HIV treatment-naïve patients were enrolled and the relationship between CD4⁺IL-21⁺T cells and Tregs were studied. The effects of IL-21 on CD4⁺CD25⁺CD127^low Tregs' apoptosis, proliferation, and CTLA-4 and TGF-β expression in HIV-infected patients was investigated and compared with the effect of other common γ-chain cytokines.

RESULTS

We found the percentage and absolute numbers of CD4⁺IL-21⁺T cells were positively related to the frequency or absolute numbers of CD4⁺CD25⁺ or CD4⁺CD25⁺CD127^low Tregs. Compared with the media-alone control, IL-21, IL-7, and IL-15 could significantly reduce apoptosis of Tregs (p<0.05). IL-21 did not promote the proliferation of Tregs as compared with media alone, while IL-2, IL-7, and IL-15 could significantly increase the proliferation of Tregs (p<0.05). IL-21 enhanced CTLA-4 expression by Tregs (p<0.05), but could not induce TGF-β secretion of Tregs from HIV infected patients. There were no significant differences of the fold induction of apoptosis, proliferation, or CTLA-4 and TGF-β expression by Tregs from HIV-infected patients and normal controls after IL-21 treatment. In vitro experiment showed that pretreatment with IL-21 significantly enhanced the suppressive effect of Tregs on CD8+ T cells' IFN-γ expression.

CONCLUSION

We conclude that IL-21 promotes the survival and CTLA-4 expression of Tregs and enhanced the suppressive capacity of Tregs during HIV infection. These results broaden the understanding of HIV pathogenesis and provide critical information for HIV interventions.

CD4 T Follicular Helper and Regulatory Cell Dynamics and Function in HIV Infection

T follicular helper cells (T_FH) are a specialized subset of CD4 T cells that reside in B cell follicles and promote B cell maturation into plasma cells and long-lived memory B cells. During chronic infection prior to the development of AIDS, HIV-1 (HIV) replication is largely concentrated in T_FH. Paradoxically, T_FH numbers are increased in early and midstages of disease, thereby promoting HIV replication and disease progression. Despite increased T_FH numbers, numerous defects in humoral immunity are detected in HIV-infected individuals, including dysregulation of B cell maturation, impaired somatic hypermutation, and low quality of antibody production despite hypergammaglobulinemia. Clinically, these defects are manifested by increased vulnerability to bacterial infections and impaired vaccine responses, neither of which is fully reversed by antiretroviral therapy (ART). Deficits in T_FH function, including reduced HIV-specific IL-21 production and low levels of co-stimulatory receptor expression, have been linked to these immune impairments. Impairments in T_FH likely contribute as well to the ability of HIV to persist and evade humoral immunity, particularly the inability to develop broadly neutralizing antibodies. In addition to direct infection of T_FH, other mechanisms that have been linked to T_FH deficits in HIV infection include upregulation of PD-L1 on germinal center B cells and augmented follicular regulatory T cell responses. Challenges to development of strategies to enhance T_FH function in HIV infection include lack of an established phenotype for memory T_FH as well as limited understanding of the relationship between peripheral T_FH and lymphoid tissue T_FH. Interventions to augment T_FH function in HIV-infected individuals could enhance immune reconstitution during ART and potentially augment cure strategies.

The Dynamics of T and B Cells in Lymph Node during Chronic HIV Infection: TFH and HIV, Unhappy Dance Partners?

Although the dynamics of germinal center (GC) formation, follicular helper T (TFH) cell recruitment to B cell follicles within lymphoid organs, and changes of lymphoid tissue architecture in HIV/SIV infection have been documented, the underlying immunopathology remains unclear. Here, we summarize what is known regarding the kinetics of TFH cells and GC B cells during the course of infection as well as the potential immunopathological features associated with structural changes in the lymphoid compartment. This review also explores the implications of cell dynamics in the formation and maintenance of viral reservoirs in hyperplastic follicles of secondary lymphoid organs before and after viral suppressive antiretroviral therapy.

A potentially protective role of IL-18 Binding Protein in HIV-infected Long-Term Non-Progressors

An imbalance between IL-18 and its antagonist, IL-18 Binding Protein, occurs in the circulation of HIV-infected individuals. We show here for the first time that HIV-infected Long Term Non-Progressors (LTNPs) do not develop this imbalance, and maintain normal levels of IL-18BP in the circulation. Their circulating levels of the antagonist correlate negatively with viral loads and show a positive trend with CD4+ T cells counts. The maintenance of normal production of IL-18BP may contribute, at least in part, to the ability of LTNPs to delay AIDS progression.

Expression of cytokine-mRNA in peripheral blood mononuclear cell of human immunodeficiency virus-1 subtype C infected individuals with opportunistic viral infections from India (South)

Human immunodeficiency virus (HIV) disease progression is associated with a marked change in the level of plasma cytokines. The study reported here investigated the level of mRNA expression of different cytokines: Tumour necrosis factor-alpha (TNF-α), interferon (INF)-gamma, interleukin-10 (IL-10) and IL-21 in the peripheral blood mononuclear cell among the antiretroviral therapy naive subtype C HIV-1 infected individuals and normal healthy controls by real time polymerase chain reaction. The mRNA expressions of all the 4 cytokines in HIV-1 infected individuals were significantly higher compared to healthy controls (P value range 0.0004-0.01). The mean level of IL-10, INF-gamma and TNF-α were higher in HIV infected individuals with low CD4 counts (<300 cells/μl). The IL-10 expression showed a significant negative correlation with CD4 counts (r=-0.25, P=0.04) while IL-21 showed a positive correlation with CD4 counts (r=0.26, P=0.03). There was a significant negative correlation between the cytomegalovirus (CMV) viral load and IL-21 expression. Cytokine levels by mRNA detection avoids the inherent problem of measuring plasma level and this study also provide information on the cytokine levels and CD4+ T cell level among HIV-1 subtype C infected individuals with opportunistic viral infections like CMV.

IL-21 and T Cell Differentiation: Consider the Context

Accumulating studies demonstrate that IL-21 modulates the differentiation of various CD4 and CD8 T cell subsets and provide insights into the underlying cellular and molecular processes that are influenced by this cytokine. Intriguingly, the effects of IL-21 on T cells can be complex and vary depending on the experimental system used. We review our current understanding of the roles of IL-21 in the generation of phenotypically distinct CD4 and CD8 T cell populations and discuss the potential environmental cues, cellular factors, and molecular mediators that impact the actions of IL-21. We propose that IL-21 acts in a context-dependent manner to accentuate T cell subset development.

Elevation and persistence of CD8 T-cells in HIV infection: the Achilles heel in the ART era

Introduction

HIV infection leads to a disturbed T-cell homeostasis, featured by a depletion of CD4 T-cells and a persistent elevation of CD8 T-cells over disease progression. Most effort of managing HIV infection has been focused on CD4 T-cell recovery, while changes in the CD8 compartment were relatively underappreciated in the past.

Methods

A comprehensive literature review of publications in English language was conducted using major electronic databases. Our search was focused on factors contributing to CD8 T-cell dynamics in HIV infection and following antiretroviral therapy (ART).

Discussion

Normalization of CD8 counts is seldom observed even with optimal CD4 recovery following long-term treatment. Initiation of ART in primary HIV infection leads to enhanced normalization of CD8 count compared with long-term ART initiated in chronic infection. Importantly, such CD8 elevation in treated HIV infection is associated with an increased risk of inflammatory non-AIDS-related clinical events independent of CD4 T-cell recovery. The mechanisms underlying CD8 persistence remain largely unknown, which may include bystander activation, exhaustion and immunosenescence of CD8 T-cells. The information provided herein will lead to a better understanding of factors associated with CD8 persistence and contribute to the development of strategies aiming at CD8 normalization.

Conclusions

Persistence of CD8 T-cell elevation in treated HIV-infected patients is associated with an increased risk of non-AIDS-related events. Now that advances in ART have led to decreased AIDS-related opportunistic diseases, more attention has been focused on reducing non-AIDS events and normalizing persistent CD8 T-cell elevation.

IL-21 Signaling in Immunity

IL-21 is a type I cytokine produced by T cells and natural killer T cells that has pleiotropic actions on a wide range of immune and non-immune cell types. Since its discovery in 2000, extensive studies on the biological actions of IL-21 have been performed in vitro and in vivo. Recent reports describing patients with primary immunodeficiency caused by mutations of IL21 or IL21R have further deepened our knowledge of the role of this cytokine in host defense. Elucidation of the molecular mechanisms that mediate IL-21's actions has provided the rationale for targeting IL-21 and IL-21 downstream mediators for therapeutic purposes. The use of next-generation sequencing technology has provided further insights into the complexity of IL-21 signaling and has identified transcription factors and co-factors involved in mediating the actions of this cytokine. In this review, we discuss recent advances in the biology and signaling of IL-21 and how this knowledge can be potentially translated into clinical settings.

Mycobacterium tuberculosis-Specific IL-21+IFN-γ+CD4+ T Cells Are Regulated by IL-12

In the current study of Mycobacterium tuberculosis (MTB)-specific T and B cells, we found that MTB-specific peptides from early secreted antigenic target-6 (ESAT-6) and culture filtrate protein-10 (CFP-10) induced the expression of IL-21 predominantly in CD4⁺ T cells. A fraction of IL-21-expressing CD4⁺ T cells simultaneously expressed Th1 cytokines but did not secrete Th2 or Th17 cytokines, suggesting that MTB-specific IL-21-expressing CD4⁺ T cells were different from Th1, Th2 and Th17 subpopulations. The majority of MTB-specific IL-21-expressing CD4⁺ T cells co-expressed IFN-γ and IL-21⁺IFN-γ⁺CD4⁺ T cells exhibited obviously polyfunctionality. In addition, MTB-specific IL-21-expressing CD4⁺ T cells displayed a CD45RO⁺CD62L^lowCCR7^lowCD40L^highICOS^high phenotype. Bcl-6-expression was significantly higher in IL-21-expressing CD4⁺ T cells than IL-21^-CD4⁺ T cells. Moreover, IL-12 could up-regulate MTB-specific IL-21 expression, especially the frequency of IL-21⁺IFN-γ⁺CD4⁺ T cells. Taken together, our results demonstrated that MTB-specific IL-21⁺IFN-γ⁺CD4⁺ T cells from local sites of tuberculosis (TB) infection could be enhanced by IL-12, which have the features of both Tfh and Th1 cells and may have an important role in local immune responses against TB infection.

Early Loss of Splenic Tfh Cells in SIV-Infected Rhesus Macaques

Follicular T helper cells (Tfh), a subset of CD4 T lymphocytes, provide crucial help to B cells in the production of antigen-specific antibodies. Although several studies have analyzed the dynamics of Tfh cells in peripheral blood and lymph nodes (LNs) during Aids, none has yet addressed the impact of SIV infection on the dynamics of Tfh cells in the spleen, the primary organ of B cell activation. We show here a significant decrease in splenic Tfh cells in SIVmac251-infected rhesus macaques (RMs) during the acute phase of infection, which persists thereafter. This profound loss is associated with lack of sustained expression of the Tfh-defining transcription factors, Bcl-6 and c-Maf but with higher expression of the repressors KLF2 and Foxo1. In this context of Tfh abortive differentiation and loss, we found decreased percentages of memory B cell subsets and lower titers of SIV-specific IgG. We further demonstrate a drastic remodeling of the lymphoid architecture of the spleen and LNs, which disrupts the crucial cell-cell interactions necessary to maintain memory B cells and Tfh cells. Finally, our data demonstrated the early infection of Tfh cells. Paradoxically, the frequencies of SIV DNA were higher in splenic Tfh cells of RMs progressing more slowly suggesting sanctuaries for SIV in the spleen. Our findings provide important information regarding the impact of HIV/SIV infection on Tfh cells, and provide new clues for future vaccine strategies.

Innate and Adaptive Immune Regulation During Chronic Viral Infections

Chronic viral infections represent a unique challenge to the infected host. Persistently replicating viruses outcompete or subvert the initial antiviral response, allowing the establishment of chronic infections that result in continuous stimulation of both the innate and adaptive immune compartments. This causes a profound reprogramming of the host immune system, including attenuation and persistent low levels of type I interferons, progressive loss (or exhaustion) of CD8(+) T cell functions, and specialization of CD4(+) T cells to produce interleukin-21 and promote antibody-mediated immunity and immune regulation. Epigenetic, transcriptional, posttranscriptional, and metabolic changes underlie this adaptation or recalibration of immune cells to the emerging new environment in order to strike an often imperfect balance between the host and the infectious pathogen. In this review we discuss the common immunological hallmarks observed across a range of different persistently replicating viruses and host species, the underlying molecular mechanisms, and the biological and clinical implications.

Regulation of CD8+ T-cell cytotoxicity in HIV-1 infection

Understanding the mechanisms involved in cellular immune responses against control of human immunodeficiency virus (HIV) infection is key to development of effective immunotherapeutic strategies against viral proliferation. Clear insights into the regulation of cytotoxic CD8+ T cells is crucial to development of effective immunotherapeutic strategies due to their unique ability to eliminate virus-infected cells during the course of infection. Here, we reviewed the roles of transcription factors, co-inhibitory molecules and regulatory cytokines following HIV infection and their potential significance in regulating the cytotoxic potentials of CD8+ T cells.

IL-21 induces antiviral microRNA-29 in CD4 T cells to limit HIV-1 infection

Initial events after exposure determine HIV-1 disease progression, underscoring a critical need to understand host mechanisms that interfere with initial viral replication. Although associated with chronic HIV-1 control, it is not known whether interleukin-21 (IL-21) contributes to early HIV-1 immunity. Here we take advantage of tractable primary human lymphoid organ aggregate cultures to show that IL-21 directly suppresses HIV-1 replication, and identify microRNA-29 (miR-29) as an antiviral factor induced by IL-21 in CD4 T cells. IL-21 promotes transcription of all miR-29 species through STAT3, whose binding to putative regulatory regions within the MIR29 gene is enriched by IL-21 signalling. Notably, exogenous IL-21 limits early HIV-1 infection in humanized mice, and lower viremia in vivo is associated with higher miR-29 expression. Together, these findings reveal a novel antiviral IL-21-miR-29 axis that promotes CD4 T-cell-intrinsic resistance to HIV-1 infection, and suggest a role for IL-21 in initial HIV-1 control in vivo.

HIV-infected patients who maintain undetectable virus levels possess elevated plasma concentrations of IL-21. Here, Adoro et al. show that IL-21 inhibits early viral infection in humanized mice and suppresses HIV-1 replication in vitro by upregulating a microRNA via the regulatory protein STAT3.

Cell-Intrinsic gp130 Signaling on CD4+ T Cells Shapes Long-Lasting Antiviral Immunity

The IL-6 cytokine family utilizes the common signal transduction molecule gp130, which can mediate a diverse range of outcomes. To clarify the role of gp130 signaling in vivo during acute viral infection, we infected Cd4-cre Il6st(fl/fl) mice, in which gp130 is conditionally ablated in T cells, with acute lymphocytic choriomeningitis virus. We found that by day 12, but not at day 8, after infection the number of virus-specific CD4(+) T cells was reduced in the absence of gp130, and this was sustained for up to 2 mo postinfection. Additionally, gp130-deficient T follicular helper cells had lower expression of Maf, IL-21, and ICOS, and this was accompanied by a reduction in the proportion of germinal center B cells and plasmablasts. Remarkably, at 2 mo postinfection the proportion of IgG2a/c(+) memory B cells and the systemic levels of lymphocytic choriomeningitis virus-specific IgG2 Abs were dramatically decreased, whereas there was a corresponding increase in IgG1(+) memory B cells and virus-specific IgG1 Abs. In the same animals gp130-deficient virus-specific CD8(+) T cells showed a reduced proportion of memory cells, which expressed lower levels of Tcf7, and displayed diminished recall responses on secondary infection. Mixed bone marrow chimeras revealed that the aforementioned gp130 effects on CD4(+) T cells were cell intrinsic. Overall, our data show that gp130 signaling in T cells influences the quantity and quality of long-lasting CD4(+) T cell responses as well as CD8(+) T cell- and Ab-mediated immunity after acute viral infection.

CD4⁺CD28null T lymphocytes resemble CD8⁺CD28null T lymphocytes in their responses to IL-15 and IL-21 in HIV-infected patients

HIV-infected individuals suffer from accelerated immunologic aging. One of the most prominent changes during T lymphocyte aging is the accumulation of CD28(null) T lymphocytes, mainly CD8(+) but also CD4(+) T lymphocytes. Enhancing the functional properties of these cells may be important because they provide antigen-specific defense against chronic infections. The objective of this study was to compare the responses of CD4(+)CD28(null) and CD8(+)CD28(null) T lymphocytes from HIV-infected patients to the immunomodulatory effects of cytokines IL-15 and IL-21. We quantified the frequencies of CD4(+)CD28(null) and CD8(+)CD28(null) T lymphocytes in peripheral blood from 110 consecutive, HIV-infected patients and 25 healthy controls. Patients showed increased frequencies of CD4(+)CD28(null) and CD8(+)CD28(null). Both subsets were positively correlated to each other and showed an inverse correlation with the absolute counts of CD4(+) T lymphocytes. Higher frequencies of HIV-specific and CMV-specific cells were found in CD28(null) than in CD28(+) T lymphocytes. Activation of STAT5 by IL-15 and STAT3 by IL-21 was higher in CD28(null) compared with CD28(+) T lymphocytes. Proliferation, expression of CD69, and IFN-γ production in CD28(null) T lymphocytes were increased after treatment with IL-15, and IL-21 potentiated most of those effects. Nevertheless, IL-21 alone reduced IFN-γ production in response to anti-CD3 stimulation but increased CD28 expression, even counteracting the inhibitory effect of IL-15. Intracytoplasmic stores of granzyme B and perforin were increased by IL-15, whereas IL-21 and simultaneous treatment with the 2 cytokines also significantly enhanced degranulation in CD4(+)CD28(null) and CD8(+)CD28(null) T lymphocytes. IL-15 and IL-21 could have a role in enhancing the effector response of CD28(null) T lymphocytes against their specific chronic antigens in HIV-infected patients.